It is known to provide a shaver or razor that relies on a laser for cutting hair rather than an arrangement of cutting blades. Shavers without blades have fewer moving parts and so wear is reduced, providing an advantage over mechanical shavers. Furthermore, the use of a laser can reduce skin irritation as there are no sharp objects that contact the skin surface. Laser shavers work by optical absorption in which hair exposed to a laser beam absorbs the energy of the beam, causing it to be vaporized and/or severed.
Shaving performance is typically measured by two criteria—closeness of shave and irritation of the skin. The cutting height is the distance between the surface of the skin and the point at which hairs are cut. A good performing shaver should minimize the cutting height and therefore minimize the remaining hair length by positioning the laser beam as close as possible to the skin. A good performing shaver should also minimize the variation in cutting height and therefore the remaining hair length should be uniform. However, positioning the laser beam close to the skin may cause more skin irritation if heat and energy from the laser is incident on the skin. It is necessary to protect the skin from contact with the laser beam to avoid damaging or irritating the skin being shaved. Hair trimmers or groomers are used to trim hair to a constant length, so although closeness is not a major performance factor, uniformity of remaining hair length is desirable.
Typically, to protect the skin from the laser and limit irritation, a comb is positioned between the laser beam and the skin to manipulate hair and limit contact between the skin and laser beam. However, this can be detrimental to the closeness of cut as it increases the distance between the skin surface and the laser beam.
It is known, for example from WO 95/33600, to provide a shaver that generates a laser beam that is positioned parallel to the skin and perpendicular to the stroke direction to cut hairs as the shaver is moved over the skin. However, Gaussian theory dictates that lasers have a natural intensity variation along their length. Beams will have a waist where the intensity and fluence are at a maximum and the beam width is at a minimum. Away from the waist, the beam width is larger and the intensity and fluence are decreased. This means that at the beam waist the energy of the laser beam is focused near to the centre of the beam, on a small area of a hair to be cut. However, away from the waist, the energy is more distributed through the beam width and therefore spread over a larger area of a hair to be cut. This variation in intensity may cause variations in the cutting height of a laser shaver with a laser beam parallel to the skin surface.